Methods for reducing chlorine dioxide associated corrosion

ABSTRACT

Methods for inhibiting chlorine dioxide associated corrosion in industrial equipment by treating industrial equipment (e.g., pipes, washers and other metallic, e.g., stainless steel surfaces) or process streams in contact with industrial equipment with one or more haloperoxidases, preferably, a chloroperoxidase, in an amount effective to reduce chlorine dioxide associated corrosion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/911,205 filed Nov. 27, 2007, which is a 35 U.S.C. 371 nationalapplication of PCT/US2006/013429 filed Apr. 11, 2006, which claimspriority or the benefit under 35 U.S.C. 119 of U.S. provisionalapplication No. 60/671,254 filed on Apr. 13, 2005, the contents of whichare fully incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to methods for reducing chlorine dioxideassociated corrosion using a haloperoxidase.

BACKGROUND OF THE INVENTION

The direct cost of corrosion in industry is estimated to be about 220billion dollars. Hays, G. 11^(th) International Symposium on Corrosionin the Pulp and Paper Industry, Jun. 7-11, Charleston, SC, 2004. Forexample, corrosion of parts and equipment is a major problem facing thepulp and paper industry due to the use of many aggressive chemicalsduring the pulp and paper making process. Among all of the chemicalsused, chlorine dioxide has the highest redox potential and is one of themost corrosive chemicals used in industry.

Many pulp and paper mills use sodium hydroxide, sulphur dioxide or otherreducing agents to remove residual chlorine dioxide from the pulp andpaper process water to reduce chlorine dioxide associated corrosion.Sodium hydroxide, however, must be used at high concentrations to beeffective and the high alkalinity can result in significant equipment anenergy costs, as well as other detrimental effects, e.g., producingcalcium carbonate scale. Although sulphur dioxide is fairly costeffective, it adds both safety hazards as well as potential corrosionproblems itself. In addition, sulphur dioxide adds sulphur to theeffluent, which may cause odor problems.

There is a need in the art for improved methods for controlling chlorinedioxide associated corrosion.

SUMMARY OF THE INVENTION

The present invention relates to methods for inhibiting chlorine dioxideassociated corrosion. In accordance with the present invention, chlorinedioxide associated corrosion may be inhibited in industrial equipment bytreating industrial equipment (e.g., pipes, washers and other metallic,e.g., stainless steel surfaces) or process water in contact withindustrial equipment with one or more haloperoxidases, preferably, achloroperoxidase, in an amount effective to reduce chlorine dioxideassociated corrosion. In an embodiment, the invention involves treatingan industrial equipment or process water following chlorine dioxidetreatment with one or more haloperoxidases, preferably, acholorperoxidase, in an amount effective to deactivate residual chlorinedioxide.

In a preferred embodiment, the industrial process is a pulp and paperprocess. Preferably, the haloperoxidase treatment is applied following achlorine dioxide treatment in the pulp and paper process, such as,following a chlorine dioxide bleaching stage, to remove residualchlorine dioxide.

DETAILED DESCRIPTION OF THE INVENTION

Chlorine dioxide is well known as an algaecide, fungicide, germicide,deodorant, bleach, and general antiseptic. Chlorine dioxide is a strongoxidizer and is widely used as a bleaching and/or disinfectant agent.Chlorine dioxide is commonly used in the pulp and paper and watertreatment industries. Chlorine dioxide is also used in considerablysmaller quantities in treating agricultural produce and certain medicalapplications. Other industrial processes which use chlorine dioxidetreatment include food and beverage production plants and confection(e.g., chewing gum) plants.

In a preferred embodiment, the present invention is applied to inhibitchlorine dioxide associated corrosion in a pulp and paper mill.Generally, pulp and paper mills include at least one chlorine dioxidetreatment process, e.g., chlorine dioxide bleaching process stage.

Any industrial equipment or process water which is subject to chlorinedioxide associated corrosion may be treated with the haloperoxidase toinhibit or prevent chlorine dioxide associated corrosion. As usedherein, industrial process stream refers to the industrial equipment(e.g., pipes, washers, etc.) or process water. Industrial equipmentwhich is subject to chlorine dioxide associated corrosion includes anymetallic surface (e.g., stainless steel) which comes in contact withchlorine dioxide and which is capable of being corroded by chlorinedioxide. Examples of industrial equipment which are commonly corroded bychlorine dioxide include pipes, washers, conduits and fittings.

The haloperoxidase is preferably applied immediately following thechlorine dioxide treatment stage, such as, by applying thehaloperoxidase to the processing water containing the chlorine dioxideafter the chlorine dioxide treatment is complete. More preferably, thehaloperoxidase is applied to the processing water that is in contactwith the industrial equipment which is subject to corrosion.

A haloperoxidase is intended to mean an enzyme selected from the groupconsisting of chloride peroxidase (EC 1.11.1.10), bromide peroxidase,and iodide peroxidase (EC 1.11.1.8). Examples of haloperoxidases includethe Vanadium haloperoxidases, as disclosed in WO 95/27046.Haloperoxidases have been isolated from various organisms: mammals,marine animals, plants, algae, a lichen, fungi and bacteria (seeBiochimica et Biophysica Acta 1161, 1993, pp. 249-256). It is generallyaccepted that haloperoxidases are the enzymes responsible for theformation of halogenated compounds in nature, although other enzymes maybe involved.

Haloperoxidases have been isolated from many different fungi, inparticular from the fungus group dematiaceous hyphomycetes, such asCaldariomyces, e.g., C. fumago, Alternaria, Curvularia, e.g., C.verruculosa and C. inaegualis, Drechslera, Ulocladium and Botrytis (see,e.g., U.S. Pat. No. 4,937,192). Haloperoxidase has also been isolatedfrom bacteria such as Pseudomonas, e.g., P. pyrrocinia (see The Journalof Biological Chemistry 263, 1988, pp. 13725-13732) and Streptomyces,e.g., S. aureofaciens (see Structural Biology 1, 1994, pp. 532-537).

According to the present invention a haloperoxidase includes thehaloperoxidase from Curvularia, in particular, C. verruculosa, such as,C. verruculosa CBS 147.63 or C. verruculosa CBS 444.70. Curvulariahaloperoxidase and recombinant production hereof is described in WO97/04102. Bromide peroxidase has been isolated from algae (see U.S. Pat.No. 4,937,192). Haloperoxidases are also described in U.S. Pat. No.6,372,465 (Novozymes A/S).

In a preferred embodiment, the haloperoxidase is a chloroperoxidase(E.C.1.11.1.10). Chloroperoxidases are known in the art and may beobtained from Streptomyces aureofaciens, Streptomyces lividans,Pseudomonas fluorescens, Caldariomyces fumago, Curvularia inaequalis,and Corallina officinalis. A preferred chloroperoxidase is thechloroperoxidase from Caldariomyces fumago (available from SIGMA,C-0278).

The concentration of the haloperoxidase may be varied in order toachieve the desired chlorine peroxide reduction. According to theinvention, the haloperoxidase will normally be added in a concentrationof 0.0001 to 100 g of protein per g of ClO₂, preferably in aconcentration of 0.001 to 10 g of enzyme protein per g of ClO₂, morepreferably, in a concentration of 0.01 to 1 g of enzyme protein per g ofClO₂. The haloperoxidase is added in an amount effective to reduceresidual chlorine dioxide (the chlorine dioxide concentration) presentfollowing a chlorine dioxide treatment process.

The haloperoxidase treatment may be applied at any appropriatetemperature and pH (such as, pH 2-10), and such temperature or pH willalso be selected based on the desired operating conditions. Thetemperature and pH should be suitable so that haloperoxidase hasappropriate activity.

The treatment time will vary depending on the process conditions.Preferably, the treatment should be for at least 1 min, more preferably,at least 30 min, and even more preferably at least 1 hr.

EXAMPLES Example 1 Chlorine Dioxide Decomposition

5 mL of 0.4 mM C10₂ was placed in several test tubes. The pH wasadjusted to 2.5 by addition of H₂SO₄. Chloroperoxidase fromCaldariomyces fumago (Sigma, C-0278) and haloperoxidase from Curvulariaverruculosa (Novozymes) were added to each test tube. The solution wasmixed and left at ambient temperature for 1 hour. The determination ofthe C10₂ concentration was made with a UV-Vis spectrometer at 359 nm.

As shown in Table 1, 5 mg of chloroperoxidase could completely decompose5 mL of 0.4 mM of ClO₂. 0.4 mM is equivalent to 27 ppm of ClO₂, which ismuch higher than the residual ClO₂ normally seen during bleaching(0.02-0.5 ppm) in a pulp and paper mill. Haloperoxidase from Curvulariaverruculosa also worked, but not nearly as effective as thechloroperoxidase. Laccases and non-haloperoxidases were also tested, butwere not able to decompose ClO₂ even at very high dose (result notshown).

TABLE 1 No. Sample Absorbency at 360 nm 1 Control (No enzyme) 0.502 2 0.1 mg Chloroperoxidase 0.408 3  0.5 mg Chloroperoxidase 0.280 4   1 mgChloroperoxidase 0.203 5   5 mg Chloroperoxidase 0 6   10 mgChloroperoxidase 0 7  200 mg haloperoxidase from 0.445 Curvulariaverruculosa 8  500 mg haloperoxidase from 0.415 Curvularia verruculosa

Example 2 Metal Coupon Corrosion Test

Metal coupons (Alabama Specialty Products, Inc. (ASPI)), made ofstainless steel (316L) were placed in 2 flasks. 200 mL of 0.4 mM ClO₂were added to each flask. Glass beads were placed in 2 flasks. The pHwas adjusted to pH 2.5 with H₂SO₄. One flask was sealed with parafilm asthe control. In addition, the flasks with the glass beads were alsosealed with parafilm. To the other flask containing the metal coupons,100 mg of chloroperoxidase from Caldariomyces fumago (Sigma, C-0278) wasadded, and the flask was then sealed. The flasks were stored at ambienttemperature for 2 weeks. The metal coupons were rinsed with distilledwater, and the number of corrosion pits generated were counted. Weightloss after drying overnight was then determined.

As shown in Table 2, chloroperoxidase effectively prevented thecorrosion of metal coupons. The ClO₂ treated control sample showedsignificant pitting on the metal surface in 2 weeks of treatment.

TABLE 2 Sample Coupon surface Treatment No. of Weight ID Finish (2weeks) Pits loss % 1 120 grit ClO₂ 5 0.113 2 120 grit ClO₂ 6 0.132 3Glass bead ClO₂ 3 0.014 4 Glass bead ClO₂ 2 0 5 120 grit ClO₂ and 0 0chloroperoxidase 6 120 grit ClO₂ and 0 0 chloroperoxidase 7 Glass beadClO₂ and 0 0 chloroperoxidase 8 Glass bead ClO₂ and 0 0 chloroperoxidase

1. A method for inhibiting chlorine-dioxide associated corrosion in anindustrial process comprising contacting an industrial process streamcomprising chlorine dioxide with one or more haloperoxidases in anamount effective to reduce the concentration of the chlorine dioxide. 2.The method of claim 1, wherein said industrial process is a paper andpulp process.
 3. The method of claim 1, wherein said contacting isperformed following a chlorine dioxide bleaching process.
 4. The methodof claim 1, wherein said contacting is performed following a chlorinedioxide disinfectant process.
 5. The method of claim 1, wherein said oneor more haloperoxidase is a chloroperoxidase.
 6. The method of claim 5,wherein said chloroperoxidase is obtained from Streptomycesaureofaciens, Streptomyces lividans, Pseudomonas fluorescens,Caldariomyces fumago, Curvularia inaequalis or Corallina officinalis. 7.The method of claim 5, wherein said chloroperoxidase is obtained fromCaldariomyces fumago.
 8. A method for inhibiting chlorine-dioxideassociated corrosion in a pulp or paper process comprising contacting aprocess stream comprising chlorine dioxide with one or morehaloperoxidases in an amount effective to reduce the concentration ofthe chlorine dioxide.
 9. The method of claim 8, wherein said contactingis performed following a chlorine dioxide bleaching process.
 10. Themethod of claim 8, wherein said one or more haloperoxidase is achloroperoxidase.
 11. The method of claim 8, wherein saidchloroperoxidase is obtained from Streptomyces aureofaciens,Streptomyces lividans, Pseudomonas fluorescens, Caldariomyces fumago,Curvularia inaequalis or Corallina officinalis.
 12. The method of claim8, wherein said chloroperoxidase is obtained from Caldariomyces fumago.